Multi-blade dosing valves, like the one described for example in U.S. Pat. No. 3,784,061, are already known.
The multi-blade dosing valve described in U.S. Pat. No. 3,784,061 comprises the following elements:    a valve body provided with a central opening crossed, in actual use, by the pulverulent or granular material, which is discharged from a hopper into a distribution duct;    a plurality of shafts, each provided with a respective blade which extends transversely to said central opening;    a motor unit, which, by rotating the plurality of shafts, causes the opening/closing of said blades to adjust the amount of material discharged from the hopper; and    a vibrator device, which can set in vibration both said valve body and said shafts provided with blades.
One of the main drawbacks of such a multi-blade dosing valve is that the energy of the vibrator device is dispersed in the valve body and does not conveniently reach the blades. This involves the formation of bridges of pulverulent material in the gaps between the blades and a lower efficiency and precision in the dosage of the material.
Furthermore, setting in vibration the entire valve body implies a remarkable noise level of the apparatus, with a consequent acoustic pollution of the work environment.